Station Spacewalks Delayed to Saturday and Wednesday

NASA International Space Station managers have delayed two spacewalks to replace a faulty cooling system component to Saturday and Wednesday.

Saturday’s spacewalk now is officially scheduled to begin at 6:55 a.m. EDT, and will be followed by a second spacewalk Wednesday to complete replacement of the ammonia pump module that failed last Saturday.

Teams of flight controllers, engineers, and spacewalk and robotics experts have made significant progress in preparing for the spacewalk, but need an additional day to finish working out all the details.

The additional time to prepare for the first spacewalk allows for the final procedures to be uplinked late today and gives the station crew one full day to review the plans that have been developed by Mission Control. Managers also moved the second spacewalk to Wednesday to give the crew additional time to rest and prepare.

During the first spacewalk the pump module will be removed and replaced. The crew will complete connecting fluid ammonia lines to the replacement pump during the second excursion Wednesday.

The spacewalks are challenging because the crew will be handling ammonia lines at full operating pressure, which makes the lines stiff during reconnection and mating. The timeline for the spacewalk will require numerous “off ramps” to ensure there is enough time to complete decontamination procedures if the crew comes in contact with ammonia.

NASA managers have stored spare pumps on the station for just this purpose, because hardware will periodically need to be replaced throughout the station’s lifetime. There are four replacement pumps on the station, delivered during previous space shuttle missions. These spares are attached to storage platforms at various locations on the station’s structure. Both the Japan Aerospace Exploration Agency’s H-II Transfer Vehicle and future commercial resupply craft will be able to deliver additional spare parts as needed.

On Wednesday, fellow astronauts Robert Satcher Jr. and Rick Sturckow were underwater, practicing the spacewalking tasks in the Johnson Space Center’s Neutral Buoyancy Laboratory (NBL). Astronauts Cady Coleman and Suni Williams spent Monday afternoon in the NBL helping to prepare for the spacewalks as well.

Robotics experts continue to refine the procedures that will be used by Walker to guide the station’s robotic arm, Canadarm2, as she moves Wheelock into position to swap the failed unit with the spare unit, stored on External Stowage Platform 2. That spare parts carrier is attached to the Quest airlock that Wheelock and Caldwell Dyson will use to exit and reenter the station.

The station’s Mobile Transporter was moved to the Starboard 1 truss on Tuesday. With the Mobile Transporter in position, the ground team will be able to gather additional data to confirm power resources are sufficient for Canadarm2 to support the spacewalk.

Each pump module weighs 780 pounds and is 5 ½ feet long (69 inches) by 4 feet wide (50 inches), and is 3 feet tall (36 inches). The spacewalkers will need to disconnect and reconnect five electrical connectors, four fluid quick-disconnect devices, one adjustable grapple bar and four bolts. The spare pump module that will be used to replace the failed unit was delivered to the station on the STS-121/Utilization Logistics Flight-1 mission in July 2006.

Wheelock, who will be designated as EV1, or extravehicular crew member 1, wearing the spacesuit bearing the red stripes, will be making the fourth spacewalk of his career. Caldwell Dyson, designated as EV2, wearing the unmarked spacesuit, will be making her first spacewalk.